The invention relates to a method and a mould for producing a concrete pipe which comprises a basic body made of concrete and a plastic inner pipe and which is intended for conducting a liquid, comprising the steps of introducing a mould core into the plastic inner pipe, introducing the plastic inner pipe into an outer mould and pouring concrete, in particular self-compacting concrete, into an intermediate space between the outer mould and the plastic inner pipe in order to form the basic body made of concrete, wherein, after the concrete has solidified, the plastic inner pipe remains as inner formwork in the basic body made of concrete and the mould core is removed after the concrete has at least partially solidified, and wherein the plastic inner pipe comprises an inner section and, at both ends, respective widened sections which have a larger cross section than the inner section.
Such concrete pipes which comprise a basic body made of concrete and a plastic inner pipe and a corresponding manufacturing method for such concrete pipes are known in the art, in particular from WO 2009/112248 A2. FIG. 1 shows by way of example a perspective diagrammatic view of a concrete pipe which is known from the prior art, comprises a basic body made of concrete and a plastic inner pipe and is intended for conducting a liquid. Said figure substantially corresponds to FIG. 1 of WO 2009/112248 A2.
The concrete pipe exemplified in FIG. 1 comprises a basic body 2 which is made of concrete and which has a substantially straight bottom side 9a and two lateral sides 9b and 9c that by way of example initially extend in straight fashion from the bottom side 9a upwards and are then bent towards each other and form a ridge 10 in the centre of the concrete pipe 1. In the area of the ridge 10, holding straps 7 are inserted by way of example in the top side of the concrete pipe 1 as transportation means for the concrete pipe 1. FIG. 1 also shows that the concrete pipe 1 has an inner diameter which is substantially circular in cross section. A corresponding plastic inner pipe 3, a so-called in-liner, is inserted or introduced into the interior of the concrete pipe 1 to protect the concrete pipe from corrosion caused by the liquid to be conducted, e.g. acid-containing waste water. Such plastic inner pipes also provide protection especially above the flow area of the waste water against caustic gases forming in the waste water, acids depositing (e.g. biogenic sulphuric acids) and bacteria which settle on the inner walls and could otherwise attack the inner surface of the concrete above the waste water.
The plastic inner pipe 3 is radially widened in both end regions of the concrete pipe 1 and thus comprises widenings 3a in the end regions. These widenings 3a have a substantially circular cross section which is larger than the cross section of the inner section of the plastic inner pipe 3 and they serve for introducing an intermediate sleeve and/or inner pipe socket into the end-sided widenings 3a of the concrete pipes 1 when two concrete pipes 1 are put together in face-sided or end-sided fashion as intended such that the intermediate sleeve and/or the inner pipe socket extends into both pipes when the ends of the concrete pipes 1 abut.
As also shown in FIG. 1, the two front sides of the concrete pipe 1 are provided by way of example with three supports 8 for bolts to receive the forces between the concrete pipes 1 substantially through the bolts when two concrete pipes 1 are put together in end-sided fashion and to simultaneously ensure a perfect positioning of the concrete pipes 1 relative to each other. This is described in detail in WO 2009/112248 A2.
According to the teaching of WO 2009/112248 A2, such concrete pipes 1 are moulded e.g. horizontally in a trough formwork as the outer mould using self-compacting concrete. According to the general teaching of WO 2009/112248 A2, thick-walled plastic inner pipes 3 are used which serve as sole shaping inner formwork for the concrete pipe 1 in the moulding process. According to a special embodiment of the manufacturing method according to the teaching of WO 2009/112248 A2, however, a mould core 4 is further introduced into the plastic inner pipe before the concrete is poured in order to stabilise and/or support the shape of the plastic inner pipe 3 during moulding. This enables the use of thin-walled plastic inner pipes 3 which would collapse and/or be deformed under the pressure of the concrete without the use of the mould core 4.
FIG. 2 schematically shows a top view of a concrete pipe 1 according to FIG. 1 in a horizontal fashion in an outer mould 5 without end-sided end plate. FIG. 3 schematically shows a longitudinal section (along section line C-C in FIG. 2) through a concrete pipe 1 comprising a basic body 2 made of concrete and a plastic inner pipe 3 according to FIG. 1, wherein a mould core 4 according to the special implementation of the method for producing the concrete pipe is introduced into the concrete pipe according to the teaching of WO 2009/112248 A2. In particular, the mould core 4 according to the teaching of WO 2009/112248 A2 is formed as an expanding core (see also FIG. 2) which consists of a steel or aluminum pipe, for example, which is provided with a longitudinal slot such that the diameter of the expanding core can be enlarged and reduced. The diameter of the expanding core is here enlarged and reduced e.g. by legs which extend to the expanding core centre and which can be reciprocated. The use of an expanding core is, however, very time-consuming and costly.
FIG. 2 and FIG. 3 illustrate the principle of a method for producing a concrete pipe 1 which comprises a basic body 2 made of concrete and a plastic inner pipe 3 and is intended for conducting a liquid, said method comprising the steps of introducing a mould core 4 into the plastic inner pipe 3, introducing the plastic inner pipe 3 into an outer mould 5 and pouring concrete into an intermediate space between the outer mould 5 and the plastic inner pipe 3 to form the basic body 2 made of concrete, wherein the plastic inner pipe 3 is retained as an inner formwork in the basic body 2 made of concrete after the concrete has solidified and the mould core 4 is removed after the concrete has at least partially solidified. The plastic inner pipe 3 comprises an inner section 3c having a substantially circular cross section and, at both ends, respective widened sections 3a and 3b which have a substantially circular cross section which is larger than the cross-section of the inner section 3c. 
It is shown in particular in FIG. 3 that the plastic inner pipe 3 has widenings 3a and 3b at its two ends, as described above, wherein the widenings serve for receiving an inner pipe socket and/or an intermediate sleeve when two concrete pipes 1 are put together. The mould core 4, however, has a cylindrical shape over its entire length and thus has a cross section over its entire length which corresponds to the cross section of the inner section 3a of the plastic inner pipe 3. Thus the widenings 3a and 3b are, however, not sealed and concrete can penetrate the widenings 3a and 3b during moulding and has to be subsequently removed in a laborious way. Moreover, it is not possible to use very thin-walled, optionally film-like plastic inner pipes 3, since the widenings 3a and 3b would be deformed by the pressure of the concrete.
It is the object of the present invention to improve the manufacturing method described in WO 2009/112248 A2 for concrete pipes which comprise a basic body made of concrete and a plastic inner pipe and to provide a more advantageous, more efficient and more cost-effective method for producing concrete pipes. In particular, an object of the present invention is in this respect to provide a method for producing a concrete pipe comprising a basic body made of concrete and a plastic inner pipe, which method serves for producing particularly durable concrete pipes having thin-walled plastic inner pipes in a more cost-effective and more efficient way.